Thursday, September 6, 2007

When volcanoes collide: Kilauea and Mauna Loa briefly (!) linked underground

Do Mauna Loa and Kilauea draw molten rock from the same source?

Geologists agree that in a larger sense they do—both gain their magma from what's called the Hawaiian plume, a place where molten rock from the earth's core punches up through the mantle of the earth to create volcanoes.

(Image at upper right, from Hawaiian Volcano Observatory, shows current eruption of Kilauea, below Pu'u 'O'o on the East Rift Zone.)

But volcano scientists have long known that chemically, the rocks erupted by Mauna Loa are different from those coming out of Kilauea. That suggests, they say, that while they may both draw from the plume, they probably draw from different places in the plume.

But a new paper says that for a brief moment in geologic time, from about 250 AD to 1400 AD, the two volcanoes were spewing largely the same stuff.

University of Hawai'i geologist Michael Garcia said that the best guess is that during that period, there was a single source that fed both volcanoes, but that both before and after that, lava produced in eruptions of the volcanoes came from different places..

“The notion is that a blob of material was under both volcanoes for a short time in the recent past,” Garcia said in an email.

“Otherwise, the sources of the two closely spaced volcanoes are distinct for many hundreds of thousands of years,” he wrote.

The July 15 issue of the journal “Earth and Planetary Science Letters” contains the paper by Jared Marske, Aaron Pietruszka, Dominique Weis and Michael Rhodes and Garcia. It is entitled, “Rapid passage of a small-scale mantle heterogeneity through the melting regions of Kilauea and Mauna Loa Volcanoes.”

Scientists use all kinds of techniques to try to envision what's under the volcanoes, and the chemistry of rocks is among them. The best assessment is that during this period, during the period Hawaiians were populating the Hawaiian archipelago, coming up from deep in the earth, “there was a filament that was large enough to be tapped by both volcanoes,” Garcia said.

The scientists studied the ratios of isotopes of three elements—lead, strontium and neodymium—in lavas of both volcanoes. Normally, the two volcanoes have distinctly different lava composition, but during the period in question, the compositions seemed to blend into each other.

“The Kilauea lavas span the (lead) isotopic divide that was previously thought to exist between these two volcanoes,” the authors write.

The lavas “moved towards an intermediate composition, and subsequently returned to typical values.”

© 2007 Jan W. TenBruggencate


Anonymous said...

This is one of the "hottest" studies ever in the history of Hawaiian petrology

Anonymous said...